Front fork

ABSTRACT

This invention provides a front fork that can be efficiently be filled with oil when it is manufactured. To achieve this object, the front fork comprising: an outer tube ( 1 ); an inner tube ( 2 ) inserted expansibly and contractibly into the outer tube ( 1 ); a double-rod damper ( 70 ) disposed inside the outer tube ( 1 ) and the inner tube ( 2 ), the double-rod damper ( 70 ) including an upper chamber ( 3   a ) and a lower chamber ( 3   b ) defined therein into which that oil is contained; and a fork-inside oil chamber ( 71 ) defined by the outer tube ( 1 ), the inner tube ( 2 ), and the double-rod damper ( 70 ), into which oil and air are contained, the front fork comprising: a check valve ( 24 ) disposed in a lower portion ( 3   b ) of the double-rod damper ( 70 ), the check valve ( 24 ) allowing only one-way flow of oil from the fork-inside oil chamber ( 71 ) to the lower chamber ( 3   b ) of the double-rod damper ( 70 ); and an air vent passage ( 25 ) of a small sectional area disposed in an upper portion of the double-rod damper ( 70 ), the air vent passage ( 25 ) communicating the upper chamber ( 3   a ) of the double-rod damper ( 70 ) with the fork-inside oil chamber ( 71 ).

FIELD OF THE INVENTION

[0001] The present invention relates to a front fork housing a dampertherein for a motor cycle. More specially, the present invention relatesto a front fork having a double-rod damper.

BACKGROUND OF THE INVENTION

[0002] Japanese Unexamined Utility Model Publication No. hei 01-80842published in 1989 by Japan Patent Office describes a front fork with adouble-rod damper where piston rods extend from both sides of a piston.

SUMMARY OF THE INVENTION

[0003] However, since in a front fork with a double-rod damper as therelated art, the double-rod damper is disposed inside an outer tube andan inner tube framing the front fork, when oil is, on a manufacturingstep of the front fork, supplied into the front fork with a pistonincorporated inside the damper, the filling of the oil is not performedefficiently, to deteriorate a work performance thereof.

[0004] Accordingly an object of the present invention is, in view of theforegoing problem, to provide a front fork into an oil chamber of whichoil can be efficiently filled.

[0005] This object of the present invention is basically attained byproviding a front fork that comprises an outer tube; an inner tubeinserted expansibly and contractibly into the outer tube; a double-roddamper disposed inside the outer tube and the inner tube, the double-roddamper including an upper chamber and a lower chamber defined thereininto which oil is contained; and

[0006] a fork-inside oil chamber defined by the outer tube, the innertube, and the double-rod damper, into which oil and air are contained.

[0007] The front fork also comprises: a check valve disposed in a lowerportion of the double-rod damper, the check valve allowing only one-wayflow of oil from the fork-inside oil chamber to the lower chamber of thedouble-rod damper; and

[0008] an air vent passage of a small sectional area disposed in anupper portion of the double-rod damper, the air vent passagecommunicating the upper chamber of the double-rod damper with thefork-inside oil chamber.

[0009] These and other objects, features, aspects and advantages of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiments of the presentinvention.

BRIEF EXPLANATION OF THE DRAWINGS

[0010]FIG. 1 is a sectional view of a front fork of a first embodimentaccording to the present invention.

[0011]FIG. 2 is a sectional view of a check valve of the firstembodiment according to the present invention.

[0012]FIG. 3 is a sectional view of a front fork of a second embodimentaccording to the present invention.

EXPLANATION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0013]FIG. 1 is a sectional view of a front fork 30 for a motor cycle ofa first embodiment according to the present invention.

[0014] The front fork 30 is formed of a cylindrical outer tube 1connected to a vehicle body (not shown), a cylindrical inner tube 2connected to a wheel (not shown) and placed inside the outer tube 1 asengaged slidably therewith, and a double-rod damper 70 arranged insidethe outer tube 1 and the inner tube 2.

[0015] A cylinder 3 is disposed coaxial with the inner tube 2 insidethereof and a piston 5 is sidably disposed inside the cylinder 3, toform the double-rod damper 70. The piston 5 divides an inside of thecylinder 3 into an upper chamber 3 a and a lower chamber 3 b, and has afirst passage 9 therein to communicate between the upper chamber 3 a andthe lower chamber 3 b. A damping valve 10 is disposed in the firstpassage 9, to control a flow amount of oil traveling through the firstpassage 9.

[0016] For example, when the piston 5 moves upward and downward insidethe cylinder 3 due to vibrations transmitted from a wheel, thevibrations are damped by resistance that the damping valve 10 gives tothe oil traveling through the first passage 9.

[0017] A first rod 6 extends from an upper face of the piston 5 andpenetrates through an upper end wall 11 of the cylinder 3 and a firstchamber 18 defined by a lid portion 16 of the outer tube 1 and the upperend wall 11 of the cylinder 3, and then a tip of the first rod 6 isconnected to the lid portion 16 of the outer tube 1. A second rod 7extends from a lower face of the piston 5 and penetrates through a lowerend wall 13 of the cylinder 3 and then a tip of the second rod 7 reachesan inside of a second chamber 4 defined by a bottom 17 of the inner tube2 and the cylinder 3. Herein the first chamber 18 and the second chamber4 forms a fork-inside oil chamber 71 described later.

[0018] A bearing 12 is disposed in the upper end wall 11 of the cylinder3 and slidably supports the first rod 6. The bearing 12 is made of ametal material such as a white metal. A seal member 8 is disposed in theupper wall 11 to be in series with the bearing 12 in an axial directionso that the oil in the upper chamber 3 a of the cylinder 3 does not leakfrom a clearance between the first rod 6 and the bearing 12.

[0019] A bearing 14 is disposed in the lower end wall 13 of the cylinder3 and slidably supports the second rod 7. The bearing 14 is made of ametal material such as a white metal. A seal member 15 disposed in thelower end wall 13 to be in series with the bearing 14 in an axialdirection so that the oil in the lower chamber 3 b of the cylinder 3does not leak from a clearance between the second rod 7 and the bearing14.

[0020] The fork-inside oil chamber 71 is defined inside the front fork30 by the outer tube 1, the inner tube 2, and the cylinder 3 where thefork-inside oil chamber 71 is a closed space the volume of which varieswith expansion and contraction of the front fork 30. The first chamber18 and the second chamber 4 forming the fork-inside oil chamber 71 asdescribed above are communicated with each other through a secondpassage 21 defined between the inner tube 2 and the cylinder 3, an upperaperture 21 a, and a lower aperture 21 b.

[0021] Oil and air are contained in the fork-inside oil chamber 71 wherethe volume therein varying with expansion and contraction of the frontfork 30 is absorbed by variations of air capacity. When the front fork30 is contracted, the air contained inside the fork-inside oil chamber71 is compressed in accordance with a stroke amount of the front fork30, and functions as an air spring.

[0022] A suspension spring 20 that bears a load acting on the front fork30 is disposed between the upper end wall 11 of the cylinder 3 and thelid portion 16 of the outer tube 1.

[0023] By constituting the double-rod damper 70 as described above, thedouble-rod damper 70 can be expanded and contracted without containingthe air into the cylinder 3 housing the piston 5. Accordingly it isprevented that the air enclosed is melted into the oil inside thecylinder 3, and as a result a characteristic of the oil changes, tobring about a change of the damping characteristic of the piston.

[0024] In the embodiment, in order to efficiently contain oil into thedamper 70 with the piston 5 being incorporated inside the cylinder 3 ata manufacturing step of the front fork 30, a third passage 22 is formedin the lower end wall 13 of the cylinder 3 so that the third passage 22supplies oil from the second chamber 4 into the lower chamber 3 b of thecylinder 3. A check valve 24 is disposed in the third passage 22, toallow only inflow of oil from the second chamber 4 into the lowerchamber 3 b of the cylinder 3 and to prevent the flow of the oil fromthe lower chamber 3 b into the second chamber 4. And an air vent passage25 of a small passage-sectional area is disposed in the cylinder 3 inthe vicinity of the upper end wall 11 thereof, to communicate between aninside (the upper chamber 3 a) of the cylinder 3 and the second passage21.

[0025]FIG. 2 is a detailed sectional view of the above-described checkvalve 24.

[0026] The check valve 24 is formed of a leaf valve, which isconstructed such that a flat member 42 is biased by a leaf spring 44disposed inside a valve housing 43, to close a port 41. When an oilpressure in the second chamber 4 is increased more than an oil pressurein the lower chamber 3 b, the oil pressure in the second chamber 4 liftsup the flat member 42, so that the oil passes through the port 41. Whenthe oil pressure in the second chamber 4 is lower than the oil pressurein the lower chamber 3 b, the flat member 42 closes the port 41, toprevent reverse flow of the oil to the second chamber 4.

[0027] Next a filling method of oil into the front fork 30 of theembodiment will be explained.

[0028] A predetermined amount of oil is supplied to the first chamber 18from an oil inlet 26 disposed in an upper portion of the first chamber18 and then the oil inlet 26 is tightly closed. In this condition theair is contained in the upper chamber 3 a and the lower chamber 3 b ofthe cylinder 3, and therefore, these chambers 3 a, 3 b inside thecylinder 3 are not filled with the oil.

[0029] The front fork 30 is attached to a tool (not shown) and isforcedly contracted by the tool. As a result the piston 5 moves toward alower side inside the cylinder 3, and the volume in the lower chamber 3b is reduced, to compress the contained air in the lower chamber 3 b. Onthe other hand, on this occasion the volume in the upper chamber 3 aexpands and pressure inside the upper chamber 3 a becomes negative.Accordingly the air in the compressed lower chamber 3 b travels throughthe first passage 9 of the piston 5 into the upper chamber 3 a.

[0030] Next the front fork 30 is forcedly expanded. The piston 5 movestoward an upper side inside the cylinder 3, and the volume in the lowerchamber 3 b expands and the pressure inside the lower chamber 3 b isreduced. As a result the check valve 24 in the third passage 22 isopened, causing the oil to flow from the second chamber 4 into the lowerchamber 3 b. On the other hand, on this occasion the volume in the upperchamber 3 a is reduced and the air in the upper chamber 3 a iscompressed, causing a part of the compressed air to be dischargedthrough the air vent passage 25 to the second passage 21. The dischargedair in the second passage 21 travels through the upper aperture 21 a tothe upper side of the first chamber 18 due to the buoyant force of theair.

[0031] In such a way, pumping of the front fork 30 continues to beperformed, the air inside the lower chamber 3 b is discharged into theupper chamber 3 a and the lower chamber 3 b is filled with the oil flownfrom the second chamber 4. As the lower chamber 3 b become filled withthe oil, the oil from the lower chamber 3 b flows through the firstpassage 9 into the upper chamber 3 a and fills the upper chamber 3 a.

[0032] By thus filling the oil, the air is easily and completelydischarged from both the upper chamber 3 a and the lower chamber 3 b ofthe cylinder 3 and each chamber 3 a, 3 b can be certainly filled withthe oil.

[0033] And by disposing the air vent passage 25 in the cylinder 3, evenif the oil inside the cylinder 3 expands due to temperature rise of theoil, the expanded oil escapes through the air vent passage 25 to thefirst chamber 18. And even if the oil in the cylinder 3 is contracteddue to temperature decrease of the oil, the oil in the first chamber 18and the second chamber 4 is pulled in through the air vent passage 25and the check valve 24 into the cylinder 3. Therefore, the pressureinside the cylinder 3 can be always held constant. As a result it is notrequired to dispose an accumulator in a piston like a conventional art,and a manufacturing cost for a front fork can be reduced by decreasingthe number of components.

[0034]FIG. 3 is a sectional view of a front fork 50 for a motor cycle ofa second embodiment according to the present invention.

[0035] In the second embodiment the cylinder 3 is formed coaxial withthe outer tube 1 inside thereof, which is spaced by a predeterminedclearance 54 in the radial direction from the outer tube 1, to define adouble-cylindrical first chamber 18 (18 a, 18 b), an inner first chamber18 a defined inside the cylinder 3, and an outer first chamber 18 bdefined between the cylinder 3 and the outer tube 1. A cylindrical leg53 extends from the upper end wall 11 of the cylinder 3 to the lidportion 16 of the outer tube 1 and connected thereto. A communicatingaperture 55 is disposed in the cylindrical leg 53 close to the lidportion 16 of the outer tube 1, and the inner first chamber 18 a and theouter first chamber 18 b are communicated through the communicatingaperture 55.

[0036] The suspension ring 20 that bears a load acting on the front fork30 is received in the second chamber 4 positioned below the cylinder 3.

[0037] The first rod 6 is not connected to the lid portion 16 of theouter tube 1 and the tip of the first rod 16 extends to the middle ofthe inner first chamber 18 a. The second rod 7 is connected to thebottom 17 of the inner tube 2.

[0038] Only the bearing 12 that supports the first rod 6 is disposed inthe upper end wall 11 of the cylinder 3 and the seal member 8 as formedin the first embodiment is not disposed. Thus the seal member 8 is notdisposed in the upper end wall 11, causing a slight clearance 51 betweenthe first rod 6 and the bearing 12. As a result, the air vent passage 25formed in the first embodiment is not disposed herein.

[0039] Components of the second embodiment other than theabove-described are identical to those in the first embodiment and arereferred to as the same numerals with the first embodiment.

[0040] In the process of filling oil, the clearance 51 performs a roleof the air vent passage 25 explained in the first embodiment. Namelywhen filling an inside of the cylinder 3 with the oil by the pumping ofthe front fork 50 as explained in the first embodiment, an aircompressed inside the upper chamber 3 a of the cylinder 3 is dischargedthrough the clearance 51 into the inner first chamber 18 a.

[0041] Thus according to the above-described construction it is alsoeasy that the air is completely discharged from the upper chamber 3 aand the lower chamber 3 b of the cylinder 3 and the oil can be certainlyfilled inside the cylinder 3.

[0042] And even if the oil inside the cylinder 3 is expanded due totemperature variations, since the expanded oil is escaped from theclearance 51 formed between the bearing 12 and the first rod 6 to thefirst chamber 18 a, the pressure in the cylinder 3 can be always keptconstant. As a result, the embodiment does not require an accumulatorlike a conventional art and reduces the number of the components used,causing reduction of a manufacturing cost for a front fork.

[0043] Further, since formation of the air vent passage 25 is notrequired, the number of manufacturing steps for the double-rod frontfork 50 can be reduced, causing reduction of a manufacturing costtherefor.

[0044] The embodiments are, as described above, explained with specificwords to some extent with regard to features of the structures andmethods thereof, but these means disclosed in this specification coverthe preferred embodiments for carrying out the present invention and itis understood that the present invention is not limited to the specificfeatures illustrated and described herein. Accordingly the presentinvention includes any modes and alternations within the scope describedin the claims that be properly construed based upon the principle ofequivalency.

What is claimed is:
 1. A front fork comprising: an outer tube; an innertube inserted expansibly and contractibly into the outer tube; adouble-rod damper disposed inside the outer tube and the inner tube, thedouble-rod damper including an upper chamber and a lower chamber definedtherein into which that oil is contained; and a fork-inside oil chamberdefined by the outer tube, the inner tube, and the double-rod damper,into which oil and air are contained, the front fork comprising: a checkvalve disposed in a lower portion of the double-rod damper, the checkvalve allowing only one-way flow of oil from the fork-inside oil chamberto the lower chamber of the double-rod damper; and an air vent passageof a small sectional area disposed in an upper portion of the double-roddamper, the air vent passage communicating the upper chamber of thedouble-rod damper with the fork-inside oil chamber.
 2. A front fork asdefined in claim 1, wherein the double-rod damper comprises: a pistonreceived in a cylinder, the piston defining the upper chamber and thelower chamber in both sides of the piston with the cylinder; a first rodconnected to one face of the piston; and a second rod connected to theother face of the piston, both the first and the second rod penetratingthrough the cylinder, and wherein the check valve is disposed in apassage communicating the lower chamber of the double-rod damper withthe fork-inside oil chamber.
 3. A front fork as defined in claim 1,wherein the fork-inside oil chamber includes an first chamber defined bythe outer tube and the cylinder, and a second chamber defined by theinner chamber and the cylinder, the check valve allows only one-way flowof oil from the second chamber of the fork-inside oil chamber to thelower chamber of the double-rod damper, and the air vent passagecommunicates the upper chamber of the double-rod damper with the secondchamber of the fork-inside oil chamber.
 4. A front fork as defined inclaim 2, wherein a bearing is disposed in the cylinder, to slidablysupport the first rod and the air vent passage is formed of a clearancebetween the first rod and the bearing, to communicate the upper chamberof the double-rod damper with the first chamber of the fork-inside oilchamber.